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1401.

Which of the following describes the hexagonal close packed arrangement of spheres ?A. ABCABAB. ABCABCC. ABABAD. ABBABB

Answer» Correct Answer - C
Discussion
1402.

In a face centred cubic lattice, atom A occupies the corner positions and atom B occupies the face centre positions. If one atoms of B is missing from one of the face centred points, the formula of the compound is :A. `AB_(2)`B. `A_(2)B_(3)`C. `A_(5)B_(5)`D. `A_(2)B`

Answer» Correct Answer - B
Contribution by atoms A on the corners
` 4= 8 xx 1/8 =1 `
Contribution by atoms B on the face centres
` 5 xx 1/2 = 5/2 `
( Total atoms on face centres = 6. As one atoms is missing , atoms actually present = 5)
: Ration of A: B = ` 1 : 5/2 = 2: 5`
Henece, formula ` = A_(2)B_(5)`
Discussion
1403.

A solid having density of `9 xx 10^(3) kg m^(-3)` forms face centred cubic crystals of edge length `200 sqrt2` pm. What is the molar mass of the solid ? [Avogadro constant `~= 6 xx 10^(23) mol^(-1), pi ~= 3`]A. `0.0432 kg mol^(-1)`B. `0.0305 kg mol^(-1)`C. `0.4320 kg mol^(-1)`D. `0.0216 kg mol^(-1)`

Answer» Correct Answer - B
Discussion
1404.

What type of crystal defect is indicated in the diagram given below : `{:(Na^(+),Cl^(-),Na^(+),Cl^(-),Na^(+),Cl^(-)),(Cl^(-),square,Cl^(-),Na^(+),square,Cl^(-)),(Na^(+),Cl^(-),square,Cl^(-),Na^(+),Cl^(-)),(Cl^(-),Na^(+),Cl^(-),Na^(+),square,N^(+)):}`A. Interstitial defectB. Schottky defectC. Frenkel defectD. Frenkel `&` Schottky defects.

Answer» Correct Answer - B
In the diagram, equal number of cations `(Na^(+))` and anions `(Cl^(-))` are missing. So it, shows schottky defect.
Discussion
1405.

The unit cell present in ABCABC, closet packing of atoms is:A. HexagonalB. tertragonalC. Face centred cubicD. primitive cubic

Answer» Correct Answer - C
Discussion
1406.

If the anion (A) form hexagonal closet packing and cation (C ) occupy only 2/3 octahedral voids in it, then the general formula of the comound is:A. CAB. `CA_(2)`C. `C_(2)A_(3)`D. `C_(3)A_(2)`

Answer» Correct Answer - C
Discussion
1407.

If the radius of the octahedral void is `r` and radius of the atom in closet packed structure is `R` thenA. `r//R=0.414`B. `r//R=0.225`C. `r//R=0.155`D. `r//R=0.732`

Answer» Correct Answer - 1
For octahedral coordination the limiting radius ratio is given as
`0.414 le r//R le 0.732`
Discussion
1408.

Hexagonal closet packed arrangement of equal -sized spheres is described byA. ABC ABA.........B. ABC ABC...............C. ABA B.............D. ABA ABB.............

Answer» Correct Answer - 3
Discussion
1409.

Hexagonal closet packed arrangement of equal -sized spheres is described byA. ABC ABCB. ABC ABCC. AB AB ABD. AB BA BA

Answer» Correct Answer - C
ABAB....... Is hexagonal close packing .
Discussion
1410.

In a face centered cubic lattice atoms A are at the corner points and atoms B at the face centered points. If atoms B is missing from one of the face centered points, the formula of the ionic compound isA. `AB_(2)`B. `A_(5)B_(2)`C. `A_(2)B_(3)`D. `A_(2)B_(5)`

Answer» Correct Answer - D
Discussion
1411.

If `a` stand for the edge length of the cube system simple cubic , body centred cubes and face centred cubic ,then the ratio of radii of the sphares in these system will be respectivelyA. `(1)/(2) a: sqrt(3)/(2)a: sqrt(2)/(2) a`B. `1a: sqrt(3a) : sqrt(2a)`C. `(1)/(2) a: sqrt(3)/(4)a: (1)/(2sqrt(2)a`D. `(1)/(2)a: sqrt(3a) : (1)/(sqrt(2) a`

Answer» Correct Answer - c
`{:(Sc,2r=a,implies,r=a//2),(bc c,4r=sqrt(3)a,implies,r=(sqrt(3)xxa)/(4)),(fc c,4r=sqrt(2)a,implies,r=a/(2sqrt(2))):}`
Discussion
1412.

In the closet packing of atoms, there are:A. one tetrahedral void and two octahedral voids per atomB. two tetrahedral voids and one octahedral void per atomC. two of each tertrahedral and octahedral voids per atomD. one of each tetrahedral and octahedral voids per atom

Answer» Correct Answer - B
Discussion
1413.

Which of the following statements are correct ?A. The co`-` ordination number of each type of ions in `CsCl` crystal is 8.B. A metal that crystallizes in `b.c.c.` structure has co`-` ordination number of `12`.C. The length of a unit cell in `NaCl` is `552p m` `(r_(Na^(+))=95p m, r_(Cl^(-))=181p m)`D. A unit cell of an ionic crystals shares some of its ions with other unit cells.

Answer» Correct Answer - a,c,d
In `b.c.c.` co`- ` ordination number si 8
Discussion
1414.

The appearance of colour in solid alkali metal halides is generally due toA. Schottky defectB. Frenkel defectC. Interstitial positionsD. F-centres

Answer» Correct Answer - D
Discussion
1415.

The appearance of colour in solid alkali metal halides is generally due toA. interstitial positionsB. F-centresC. Schottky defectD. Frenkel defect

Answer» Correct Answer - B
The colour is due to F-centres created by the electrons present in the holes
Discussion
1416.

The appearance of colour in solid alkali metal halides is generally due toA. Interstital positionsB. F- centresC. Schottky defectD. Frenkel defect

Answer» Correct Answer - 2
Alkali halides like `NaCl` and `KCl` show metal excess defect due to anionic vacancies ,When crystal of `NaCl` are heated in an atmosphere of sodium vapour the sodium atoms are depostied on the surface of the crystal . The `Cl^(-)` ions diffuse to the surface of the crystal and combine with `Na` atoms to give `NaCl`. This happens by loss of Valance electron by `Na` atoms to form `Na^(+)` ions. The relased electrons diffuse into the crystal and occupy anionic sites.
As a result the crystal now has an excess of sodium . The anionic sites occupied by unpaired electrons are called `F` -centres ( form the German word, Farbenzenter for colour centre). They impact yellow colour to the crystals of `NaCl`. The colour results by excitaiton of these electorns when they absorb energy from the visible light falling ont eh crystals. Similarly excess of `Li` makes `LiCi` crystals pink, and excess of `K` makes `KCl` crystal violet (or lilac).
Discussion
1417.

If `a ` stands for the edge length of the cubic system `:` simple cubic, body `-` centred cubic anf face `-` centred cubic, then the ratio of radii of the spheres in these systems will be respectively`:`A. `(a)/(2):(asqrt(3))/(2):(asqrt(2))/(2)`B. `1a:sqrt(3)a:sqrt(2)a`C. `(a)/(2):(asqrt(3))/(4):(a)/(2sqrt(2))`D. `(a)/(2):sqrt(3)a:(a)/(sqrt(2))`

Answer» Correct Answer - c
For simple cubic,
`(r^(+))/(r^(-))=(a)/(2) (` where `a` is edge length `)`
For `b.c.c.,(r^(+))/(r^(-))=(asqrt(3))/(4)`
For `b.c.c.,(r^(+))/(r^(-))=(a)/(2sqrt(2))`
Discussion
1418.

Which of the following figures represets the cross-section of an octahedral site?A. B. C. D.

Answer» Correct Answer - D
Discussion
1419.

The appearance of colour in solide state of alkali metal halides is generally due to `:`A. Frenkel defectB. Interstitial positionsC. `F-`centresD. Schottky defect

Answer» Correct Answer - c
Presence of excess `Na ` in `NaCl` makes it yellow, presence of excess `Li` in `LiCl` makes it pink, presence of excess `K` in `KCl` makes it violet. Greater the no. of `F-` centres, greater is intensity of colour.
Discussion
1420.

If `r` is the radius of the octahedral voids and `R` is the radius of the atom in close packing,then `:`A. `(R)/(r)=9.1`B. `(R)/(r)=3.22`C. `(R)/(r)=2.41`D. `(R)/(r)=4.67`

Answer» Correct Answer - d
`AC=sqrt(AB^(2)+BC^(2))`
`=(2R)^(2)+(2R)^(2)` ltBRgt `R+R+2r=2sqrt(2R)`
`2r=2(sqrt(2R)-R)`
`=r=(sqrt(2)-1)R`
`(r)/(R)=0.41`
`:. (R)/(r)=2.41`
Discussion
1421.

Which of the following figures represents the cross section of an `OV`?A. B. C. D.

Answer» Correct Answer - d
The octahedral holes are surrounded by six spheres arranged at the corners of an octahedron.
Discussion
1422.

Arsenic is used to dope germanium to obtainA. intrinsic semiconductorB. p-type semiconductorsC. n-type semiconductorsD. non-conducting germanium

Answer» Correct Answer - C
Discussion
1423.

The `Ca^(2+)` and `F^(-)` ions located in `CaF_(2)` crystal respectively at `f.c.c.` lattice points and in`:`A. octahedral voidsB. tetrahedral voidsC. half of octahedral voidsD. half of tetrahedral voids

Answer» Correct Answer - b
In `CaF_(2)`, the `Ca^(2+)` ions are present at all the corners and the centre of each face of the cube. The `F^(-)` ions occupy the tetrahedral sites.
Discussion
1424.

What is the C.N of `Ca^(2+)` and `F^(-)` ions in `CaF_(2)` crystal lattice ?A. C.N of `Ca^(2+)=4` and `F^(-)=8`B. C.N of `Ca^(2+)=6` and `F^(-)=6`C. C.N of `Ca^(2+)=8` and `F^(-)=8`D. C.N of `Ca^(2+)=8` and `F^(-)=4`

Answer» Correct Answer - D
Each `Ca^(2+)` ion is surrounded by `8F^(-)` ions and `F^(-)` ion by `4Ca^(2+)` ions. Thus, the C.N. of `Ca^(2+)=8` and of `F^(-)=4` in `CaF_(2)`
Discussion
1425.

An element crystallises in a faces centered cubic lattice. Hence, its unit cell containsA. 14 atoms of the element and 8 of them belong to the unit cellB. 14 atoms of the element and 4 of them belongs to the unit cellC. 8 atoms of the unit cell and only 1 of them belongs to the cellD. 8 atoms of the unit cell and only 2 of them belong to the cell

Answer» Correct Answer - B
Discussion
1426.

The `Ca^(2+)` and `F^(-)` ions arc located in `CaF_(2)` crystal respectively at face centred cubic lattice points and inA. Tetrahedral voidsB. Half of tetrahedral voidsC. Octahedral voidsD. Half of octahedral voids.

Answer» Correct Answer - A
Discussion
1427.

A group `IV` A element with a density of `11.35 g//cm^(3)` crystallises in a face centered cubic lattice whose unit cell edge length is `4.95 Å` .Calculate its atomic massA. `207.2 g//mol`B. `180 g//mol`C. `109.9 g//mol`D. `280.8 g//mol`

Answer» Correct Answer - d
`d = (GAM xx Z)/(N_(A) xx a^(3))`
for `PC C,Z = 4`
`GMA = 207.2 g//mol`
Discussion
1428.

The maximum percentage of available volume that can be filled in a face centred cubic system by atoms isA. 0.74B. 0.86C. 0.34D. 0.26

Answer» Correct Answer - A
Discussion
1429.

What is the number of atoms in a unit cell of face-centred cubic crystal ?A. 4B. 6C. 2D. 1

Answer» Correct Answer - A
Discussion
1430.

A crystal is made of particles X,Y and Z.X form fcc packing . Y occupies all the octahedral void of X and Z occupies all the tetrahedral voids of X . If all the particles along one body diagonal are removed then the formula of the crystal would be:A. `XYZ_(2)`B. `X_(2)YZ_(2)`C. `X_(8)YT_(4)Z_(5)`D.

Answer» Correct Answer - D
Discussion
1431.

A swubstance `A_(x)B_(y)` crystallises in a face cubic centred cubic (fcc) lattice in which `A` occupy each corner of the cube and atoms `B` occapy the centers of each face of the ci=ube identical the correct composition of the substance `A_(x)B_(y)`A. `AB_(3)`B. `A_(4)B_(3)`C. `A_(3)B`D. composition cannot be specified

Answer» Correct Answer - a
Effective number of corrent atom `(A) = A xx (1)/(8) = 1 = X`
Effective number of face corrent atom `(B)`
`= (1)/(2) xx 6 = 3 = Y`
Thus composition of substance` = AB_(3)`
Discussion
1432.

In a face centerd cubic cell, the contribution of an atom at a face of the unit cell is:A. `(1)/(4)`B. `1`C. `(1)/(2)`D. `(1)/(8)`

Answer» Correct Answer - B
bcc structure has one atom shared by 1 unit cell.
Discussion
1433.

Copper crystallises in a structure of face centerd cubic unit cell. The atomic radius of copper is `.28 Å`. What is axial length on an edge of copper ?A. `2.16Å`B. `3.62Å`C. `3.94Å`D. `4.15Å`

Answer» Correct Answer - B
Discussion
1434.

In fcc lattice ,A, B, C,D atoms are arranged at corner , face centre , ocatahedral void and tetrahedral void respectively , then the body diagonal contains :A. `2A,C,2D`B. `2A, 2B , 2C`C. `2A, 2B,D`D. `2A,2D`

Answer» Correct Answer - A
Discussion
1435.

Assertion: Diamond has a ccp arrangement in which corners, face centres and alternate tetrahedral holes are occupied by C atoms Reason: In diamond, C atoms at corners are `sp^(3)` hybridised but at the face centres these are `sp^(2)` hybridisedA. If both assertion and reason are correct and reason is correct explanation for assertionB. If both assertion and reason are correct but reason is not correct explanation for assertionC. If assertion is correct but reason is incorrectD. If both assertion and reason are incorrect

Answer» Correct Answer - C
Correct Reason In diamond all C atoms are `sp^(3)` hybridised
Discussion
1436.

In a face centerd lattice of `X` and `YX` atoms are present at the corners while `Y` atom are at face centers .Then the formula of the compound isA. `XY_(3)`B. `X_(2)Y_(3)`C. `X_(3)Y`D. `XY`

Answer» Correct Answer - a
For `X,8 xx (1)/(8) = 1`
For `X, 6 xx (1)/(2) = 3`
so `XY_(3)`
Discussion
1437.

The unit cell of a binary compound of A and B has ccp structure with A atoms occupying the corners and B atoms occupying the centres of each face of the unit cell. If during crystallisation of the alloy, in the unit cell two atoms of A are missing, the overall composition per unit cell is :A. `AB_6`B. `AB_4`C. `AB_8`D. `A_6B_24`

Answer» Correct Answer - D
Permitted coordination number for ccp is 8 , but 2A atoms are missing
`therefore " Contribution of A `=6xx1/8=6/8`
Contribution of B `=6xx1/2=3, " So" , A_(6//8)B_3 " or " A_6B_(24)`
Discussion
1438.

In a face centered lattice of X and Y, X atoms are present at the corners while Y atoms are at face centers. Then the formula of the compound would be if one of the X atoms is missing from a corner in each unit cell:A. `X_(7)Y_(24)`B. `X_(24)Y_(7)`C. `XY_(24)`D. `X_(24)Y`

Answer» Correct Answer - A
No. of X atom per unit cell `= 7 xx (1)/(8) = (7)/(8)`
No. of Y atom per unit cell `= 6 xx (1)/(2) = 3`
`:.` Formula `= X_(7//8) Y_(3) " or " X_(7) Y_(24)`
Discussion
1439.

What is the nearest distance between two different layers in ABAB arrangement (`a = 2 xx` radius of the particle)A. `sqrt((8)/(3))a`B. `sqrt((4)/(3))a`C. `(1)/(sqrt6) a`D. `sqrt((2)/(3))a`

Answer» Correct Answer - D
Discussion
1440.

In a CCP lattice of X and Y,X atoms are present at the corners while Y atoms are at face centers. Then the formula of the compound would be if one of the X atoms from a corner is replaced by Z atoms (also monovalent) ?A. `X_(7)Y_(24)Z_(2)`B. `X_(7)Y_(24)Z`C. `X_(24)Y_(7)Z`D. `XY_(24)Z`

Answer» Correct Answer - B
Discussion
1441.

In a simple cubic lattice of anions, the side length of the unit cell is `2.88 Å`. The diameter of the void in the body centre isA. `1.934 Å`B. `0.461Å`C. `2.108Å`D. `4.988Å`

Answer» Correct Answer - C
Discussion
1442.

You are given 6 identical balls. What is the maximum number of square voids and triangular voids (in separate arrangements) that can be created ?A. 2,4B. 4,2C. 4,3D. 3,4

Answer» Correct Answer - A
Discussion
1443.

Ice crystallises in a hexagonal lattice having a volume of the unit cell as ` 132 xx 10^(-24) cm^(3)` . If density of ice at the given temperature is 0.92 `g cm^(-3)`, the number of ` H_(2)O` molecules per unit cell isA. 1B. 2C. 3D. 4

Answer» Correct Answer - b
` p = ( Z xx M)/(a^(3) xxN_(0)) ` , the aim is to find Z.
` 0.92 = ( Z xx 18)/((132 xx 10^(-24)) ( 6.02 xx 10^(23))) `
` ( Z xx 18) /(132 xx 6.02 xx 10^(-1))`
`or Z = ( 0.92 xx 132 xx 6.02 xx 10^(-1))/18 = 4.06`
Discussion
1444.

In which of the following arrangements, Octahedral voids are formed ?A. hcpB. bccC. simple cubicD. fcc

Answer» Correct Answer - A,D
In hcp and fcc arrangement, octahedral voids are formed. In fcc, the octahedral voids are observed at edge and centre of cube while in bcc and simple cubic, no any octahedral voids are observed. In bcc, cubic voids formed.
Discussion
1445.

Sodium metal crystallizes in a body centred cubic lattice with a unit cell edge of 4.29 Ã…. The radius of sodium atom is approximately :A. `5.72overset(@)A`B. `0.93overset(@)A`C. `1.86overset(@)A`D. `4.29overset(@)A`

Answer» Correct Answer - 3
For bcc, `r=sqrt(3)/(4)a, r=sqrt(3)/(4)xx4.29=1.86overset(@)A`
Discussion
1446.

A metal crystallizes with a face- centred cubic lattice. The edge of the unit cell is 408 pm. The diameter of the metal atom isA. 288 pmB. 408 pmC. 144 pmD. 204 pm

Answer» Correct Answer - C
For fcc,lattice , ` r = a/(2sqrt2) = 0.3535 a `
= `0.3535 xx 408 "pm" = 144 "pm"`
Diameter = 2 r = 288 pm.
Discussion
1447.

Sodium metal crystallizes in a body centred cubic lattice with a unit cell edge of 4.29 Ã…. The radius of sodium atom is approximately :A. `1.86 overset(@)A`B. `3.22 overset(@)A`C. `5.72 overset(@)A`D. `0.93 overset(@)A`

Answer» Correct Answer - A
`R=sqrt(3)/(4)a=1.86overset(@)A`
Discussion
1448.

Sodium metal crystallizes in body centred cubic lattice with the cell edge, `a=4.29Å`. What is the radius of sodium atom?A. `1.86 Å`B. `3.22Å`C. `5.72Å`D. `0.93Å`

Answer» Correct Answer - A
Discussion
1449.

In a face centered cubic cell , an the face contributes in the unit cellA. 1/4 partB. 1/8 partC. 1 partD. 1/2 part.

Answer» Correct Answer - D
Face centred cubic structure contribute of 1/8 by each atom present on the corner and 1/2 by each atom present on the face.
Discussion
1450.

The number of atoms is 100 g of a fcc crystal with density = 10.0 ` g//cm^(3)` and cell edge equal to 200 pm is equal toA. ` 5 xx 10^(24)`B. ` 5 xx 10^(25)`C. ` 6 xx 10^(23)`D. ` 2 xx 10^(25)`

Answer» Correct Answer - d
` p = ( Z xx M)/(a^(3) xx 10^(-30) xx N_(0))`
` or M= ( 10 xx (200)^(3) xx 10^(-30) xx 6 xx 10^(23))/4 = 12`
Thus, 12 g contain = ` N_(0)= 6 xx 10^(23) ` atoms
100 g will contain = `( 6 xx 10^(23))/12 x 100 = 5 xx 10^(24)`
Discussion